The field of the invention is imaging methods and systems. More particularly, the invention relates to a multi-plane graphic prescription interface and method for an imaging system.
Imaging systems are commonly employed to allow an operator to obtain images that show the interior of a structure of interest. A common application of such imaging systems is medical imaging, and a common approach for implementing such imaging systems, especially in the context of medical imaging, is magnetic resonance imaging.
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field Bz), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. A net magnetic moment Mz is produced in the direction of the polarizing field, but the randomly oriented magnetic components in the perpendicular, or transverse, plane (x-y plane) cancel one another. If, however, the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, Mz, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment M1, which is rotating, or spinning, in the x-y plane at the Larmor frequency. The degree to which the net magnetic moment Mz is tipped, and hence the magnitude of the net transverse magnetic moment M1 depends primarily on the length of time and the magnitude of the applied excitation field B1. A signal is emitted by the excited spins, and after the excitation signal B1 is terminated, this signal may be received and processed to form an image.
When utilizing MRI to produce images, a technique is employed to obtain MRI signals from specific locations in the subject. Typically, the region which is to be imaged is scanned by a sequence of MRI measurement cycles which vary according to the particular localization method being used. The resulting set of received MRI signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques. To perform such a scan, it is, of course, necessary to elicit MRI signals from specific locations in the subject. This is accomplished by employing magnetic fields (Gx, Gy, and Gz) which have the same direction as the polarizing field B0, but which have a gradient along the respective x, y and z axes. By controlling the strength of these gradients during each MRI cycle, the spatial distribution of spin excitation can be controlled and the location of the resulting MRI signals can be identified.
In order for an MRI system to acquire signals from a region of interest to an operator, it is necessary for the operator to first prescribe the acquisition that is to be performed, including inputting parameters such as the field of view, spacing and thickness, as well as the orientation and location of the desired image or images. In general, it is desirable for the operator to be able to optimally perform the prescription such that the prescribed image accurately encompasses the region of interest.
Graphic prescription is a technique that allows an operator to perform a prescription using graphic techniques. Typically, to perform a graphic prescription, reference localizer images are first obtained and the operator is then allowed to mark the localizer images with prescription marks such as points, lines, boxes or other shapes, and to manipulate the marks until the desired prescription is achieved. It is desirable for the prescription interface to allow the operator to operate in a manner that is efficient and that results in the operator making an accurate prescription. However, when imaging the interior of a three-dimensional structure, it is often difficult for the operator to visualize the orientation of the prescribed spatial information, particularly in double oblique cases. Even if multiple localizer images are displayed, the three-dimensional orientation of the prescribed spatial information is not always obvious and, therefore, inaccurate prescriptions often result.